Fertilization of partially jellied and jellyless oocytes of the frog Rana pipiens

The oocyte of Rana pipiens is coated by three visible jelly layers designated V1, V2, and V3 from inner to outer. Oocytes with V1 were rarely fertilized, while oocytes with V1 and V2, V1 and V3, and V3 were fertilized. Oocytes with V1 and V3 lost their fertilizability more rapidly after being placed in 10% Ringer's than did oocytes with V1, V2, and V3. When jellied oocytes were dejellied with KCN, they were not fertilized on insemination. The addition of a water extract of jellied oocytes (egg‐water) insured fertilization of dejellied oocytes. The finding that the factors necessary for fertilization are diffusible decreases the importance of locating them in a given jelly layer. The activity of the egg‐water survived lyophilization and was heatlabile. Both a dialyzable and a non‐dialyzable fraction were required to insure a high frequency of fertilization. Egg‐water had to be present with the sperm and the oocytes in order for fertilization to occur. Sperm incubated in egg‐water lost their fertilizing ability with time. Mature body cavity oocytes, which had not been coated with jelly by the oviduct, were fertilized at a low frequency under the same conditions that resulted in a high frequency of fertilization of dejellied oocytes. Similarly, dejellied oocytes of the toad Bufo americanus were fertilized in toad or frog egg‐water, while body cavity toad oocytes were not fertilized.